The sealing of metal components of a fluid-containing product wherein fluids are to be maintained within the product, such as a fluid electrolyte-containing battery, requires particularly effective design of sealing members present at the interface of components. Otherwise, the interface might provide a passage for undesirable fluid leakage.
The recent increase in small electrically-powered devices has increased the demand for very small electrochemical cells, usually disc-like or pellet-like in appearance. These cells, often called "button cells", usually have diameters ranging up to about 1.0 inch and heights ranging up to about 0.60 inches. Because of the minute size of these cells each cell component must be manufactured with substantial precision to meet the geometric tolerances both of the device into which the cell will be placed and to provide a good fit with other components, thus reducing leakage of corrosive electrolytes. A poor seal may impede the effectiveness of a battery and/or allow leakage which may be damaging to devices into which the battery is placed. Because button cells and the like are being utilized in increasingly more sophisticated devices, it is becoming increasingly more important to provide a substantially leakproof design. Accordingly, several methods to provide leakproof button cells have been utilized. However, to date the attempts to provide leakproof designs have not been entirely successful.
An example is shown in Jaggard, U.S. Pat. No. 3,897,265 (which recently reissued as U.S. Pat. No. Re. 31,413). Jaggard discloses a method of sealing zinc-air electrochemical button cells which utilize "a single insulating and sealing member having an L-shaped cross-section," (Claim 1, Col. 7, lines 41-42). As disclosed in Jaggard, the portion of the sealing grommet which contacts the outer anode can (i.e.. the long side of the L) has a uniform thickness. Variations of such L-shaped sealing grommets, including "J-shaped" sealing grommets are known and utilized in the industry. Such well known seal grommets, while providing some resistance to cell leakage, cause several problems during the assembly of button cells.
Because of their shape, in order to prevent leakage of electrolyte, grommets such as disclosed in Jaggard must be manufactured according to very strict specifications. Such exacting manufacturing specifications in a plant setting often result in equipment failure, the rejection of a large quantity of manufactured parts because of only minor defects, or in a bottleneck in the entire button cell manufacturing process.
The straight side wall of prior art grommets mandates that other cell components which contact the grommet, such as the sidewalls of the cathode cannister, be manufactured to within very narrow tolerances. This may necessitate that cell parts only slightly damaged during manufacture or handling, be rejected in order to reduce the possibility of leakage.
It is common during mass production of small electrochemical cells to effect a preliminary assembly of the various components of the cells prior to the final closing of the cell. Final closing may involve applying sufficient pressure to press together appropriate components of the cell, together with substantially simultaneous crimping of cannister edges to lock components into place. During preliminary assembly, the degree to which component parts are pressed together prior to final sealing varies widely from cell to cell causing the cells to be of non-uniform height prior to final closing. This lack of uniformity may render the final sealing operation less efficient than would be the case if the preassembled cells were of uniform height.
When electrolytic fluids and the like are present within the cells, it is possible for fluid to splash out during the preliminary assembly process. This may be caused by a number of mechanisms including for instance, distortion of components or of container walls and the like within the cell causing inadvertent indentation of surfaces or insertion of members into the volume occupied by fluids, thus forcing the fluids out of the cell. For instance, pressure on the anode cap of a battery cell may cause the base of the cap to indent into the inner volume of the anode thus forcing anode fluids out of the cell. Also, pressure at interfaces between anode and cathode components may force cathode components into the anode volume causing the same result. Splashed out electrolyte may cause cells to stick to automated equipment, for instance, to a closing die during final closing of the cell. This may necessitate shutting down the automated cell closing equipment in order to clear the die. Moreover, cell electrolyte often discolors the outside of the cell creating associated problems with consumer appeal.
Accordingly, it is an object of the present invention to provide a reliable sealing member which is effective to retard the passage of fluids at the interface of component parts of fluid-containing products wherein the sealing member is sandwiched between the component parts.
It is another object of the invention to provide a grommet for use in batteries, and particularly for use in small electrochemical cells such as button cells, which allows for simplified and efficient cell assembly.
It is another object of the invention to provide a grommet for use in batteries, and particularly for use in small electrochemical cells such as button cells, which allows economical mass production of the cells with low incidence of equipment shut down.
It is another object of the invention to provide battery cells which effectively resist leakage of electrolyte.
It is yet another object of the invention to provide flexible sealing members for battery cells which retard the splash out of battery fluids during assembly.
These and other objects will become apparent from a thorough reading of the instant disclosure.